As a ferrule to hold end portions of optical fibers, there has been known the following ferrule. The ferrule includes an adhesive-filling section having an opening from which an adhesive is filled. The adhesive is filled in the adhesive-filling section to fix the optical fibers. Patent Literature 1 discloses that an adhesive is filled and hardened in an adhesive-filling section while end surfaces of optical fibers are caused to abut onto an inner wall of the adhesive-filling section of a ferrule.